Thermo Products GMC-85, OMC-70 service manual Electrical Branch Supply Circuit

All installations and services must be performed by qualified service personnel.

1.Electrical Branch Supply Circuit

Route all electrical wiring to the left side of the furnace. The power supply circuit to the furnace must be installed and grounded in accordance with the provisions of the National Electrical Code, ANSI/NFPA-70-1999, or latest edition, and all local codes having jurisdiction.

2.Connection Of Power Supply Wires

a.Remove the furnace control panel cover.

b.Insert 120 VAC wires through the strain relief bushing (or conduit connection as applicable) on the left side of the furnace junction box.

c.Connect the “Hot” wire to the terminal block lug marked “L1”.

d.Connect the “Neutral” wire to the terminal block lug marked “L2”.

e.Connect the “ground” wire to the terminal block lug marked “G”.

f.Reinstall and secure the control panel cover with the original mounting screws.

3.Connection Of Thermostat Wires

NOTE: Class 1 thermostat wire must be used inside the furnace burner compartment.

a.Insert 24 VAC wires through the plastic grommet on the left side of the furnace casing.

b.Connect the thermostat wires to the yellow leads from the burner (refer to the applicable wiring diagram).

c.Connect the thermostat wires to the room thermostat.

IMPORTANT: The room thermostat should be installed 4 to 5 feet above the floor on interior wall which is relatively free from direct sources of heat (sunlight or supply airflow) or exposure to cold (drafts from open windows and doors). The nominal anticipator settings are 0.8 amperes, for the GMC, and 0.2 amperes, for the OMC (refer to the thermostat literature for additional information).

Five-conductor thermostat wire is recommended for 24 VAC, low-voltage, control circuit wiring. Only 2 wires are required for the furnace (a heating application only).

Electrical Wire Diameter

(AWG)

24

22

20

18

Maximum Recommended Thermostat Wire Length

(feet)

55

90

140

225

24